Android tablet computers will grow from 32 percent global market share in the third quarter to an estimated 40.3 percent through the fourth quarter, reducing Apple's iPad share to 59 percent, projects IDC. The growth in Android tablets is due largely to the popularity of the low-cost Kindle Fire and Nook Tablet, says the study.

Amazon's Kindle Fire and Barnes & Noble's Nook Tablet (pictured) will power Google's Android platform to 40.3 percent media tablet market share in the fourth quarter of 2011, projects IDC. That's up from 32.4 percent in Q3, according to the research firm.

Apple, which established the market and set a high bar with its popular iPad, shipped 11.1 million of the devices in Q3. That's good for 61.5 percent worldwide market share, but down from 63.3 percent in Q2. Apple's share is projected to drop to 59 percent in the fourth quarter.

In a breakdown by vendor, Samsung took 5.6 percent market share for second place with its Galaxy Tab tablets, and HP also nibbled at the iPad's market share in the third quarter, selling over 900,000 TouchPads to take five percent share for third place. HP's placement was accomplished by discounting the soon to be discontinued WebOS-based slate to $99.

Barnes & Noble, meanwhile, took third place with 4.5 percent share, selling over 800,000 of its Android-powered Nook Color electronic readers in the third quarter. IDC began counting the color e-reader as a media tablet last quarter. Asus, which sells a Eee Pad Transformer tablet (pictured), rounded out the top five with a 4 percent share.

IDC estimated the media tablet market grew 24 percent on a sequential basis to 18.1 million units for the third quarter. For an idea of how the tablet market has ballooned, that unit shipment total is higher than the 18 million units sold in all of 2010, according to IDC's count. While that represents an increase of 264.5 percent from the same quarter last year, it's 5.8 percent below the original forecast of 19.2 million units.

The market researcher is seeing such strong demand for tablets in the fourth quarter, however, that it has boosted its worldwide shipment forecast for 2011 to 63.3 million units, up from its previous tally of 62.5 million units.

Android will also significantly ding Research In Motion's PlayBook, which IDC sees slipping from 1.1 percent share in the third quarter to 0.7 percent share through the end of the year.

IDC analyst Tom Mainelli stated, "Amazon and Barnes & Noble are shaking up the media tablet market, and their success helps prove that there is an appetite for media tablets beyond Apple's iPad."

Financial analysts are modeling Amazon to sell anywhere from four million to six million Kindle Fire units in 2011, with Amazon now claiming that the $200 device is selling more than a million units per week. The $250 Nook Tablet is also expected to sell well this holiday quarter.

By comparison, the iPad starts at $500. IDC expects additional low-cost Android tablets to pressure the iPad more than any high-end Android tablet.

However, don't expect the iPad to lose too much share. IDC expects Q4 to be Apple's best quarter for the iPad. The iPad racking up market share in the enterprise and education sectors and an iPad 3 certainly on the way in early 2012. Meanwhile, Apple is rumored to be considering a smaller 7.85-inch model to go along with the 9.7-inch version.